While we like to think of ourselves as “human,” much of what we call “ourselves” is really composed of microbes — about 100 trillion of them, to be exact. And our guts are no exception. Instead of “You are what you eat,” it might actually be more accurate to say, “You are what your microbes eat.”

Scientists now believe that people may have distinctly different gut microbe types, in the same way that people have different blood types. These different microbe ecosystems begin at birth.

In fact, scientists have shown that babies born by cesarean section actually develop different and less diverse microflora than babies born naturally. And babies fed formula have more abundant bacteria in their stools than their breast-fed counterparts. It seems that passage through the birth canal plus mother’s milk both offer beneficial bacteria to babies, and differences in these exterior events can cause changes in the intestines.

Diversity in digestive microbes continues into adulthood. Scientists have reported that they’ve found three distinct ecosystems of microflora in the guts of adults. Each ecosystem has a distinct group of microbial species. When examining the patients and their gut microbes, they could not find correlations with health, sex, age ethnicity or weight, so they are pursuing other theories — including that different microbes colonize the guts of infants at birth.

The discovery of these different ecosystems — called enterotypes (EN-tuh-ro-type) — may allow physicians to one day tailor drug prescriptions or dietary advice to meet a patient’s individual gastrointestinal needs.

So the next time you have an insatiable craving for chocolate or an aversion to spinach, remember — it may be your microbes talking.